There are already low cost disposable syringes made of plastic materials, such as polypropylene and the like, which have replaced almost completely the older ones made of glass, thus eliminating the sterilization problems that the older type used to have.
Nevertheless, since this type of syringe retains all its functional characteristics after use, except of course for not being sterile, their being disposable depends only on the will of the user and for this reason they are not strictly single use, since they may be re-utilized by unscrupulous users.
The huge health problem posed by spreading infectious diseases by this means is well known, and the increase in dangerous diseases like viral hepatitis and acquired immune deficiency syndrome (AIDS) in persons that share and reuse syringes is a particularly troublesome problem. This means of contamination, however, is not limited exclusively to unscrupulous users who re-utilize syringes; accidental punctures among health professionals are very common, caused by the needles of syringes that have already been used with patients.
There have been other attempts heretofore to ameliorate the aforementioned problems. There is a disposable syringe that can be rendered unusuable after its use through the voluntary rupture of the stem of its plunger, as represented by the Spanish Utility Model No. 229607 granted to DEXA, S.A. Hypodermic syringes with sheaths for protection of the needle are also known.
Nevertheless, the solutions known up to now do not guarantee the resolution of the aforesaid problems. Concerning un-reusability after use of the hypodermic syringe in the Spanish model of the DEXA, S.A. company aforementioned, it is a syringe the plunger part of which comprises a stem that may be ruptured due to a weakening in the material of said stem, so that the syringe will be rendered unusable only depending on the will of the user, that is to say, it may be rendered permanently unusable provided the user so desires and takes the necessary action, and this evidently does not happen with unscrupulous users such as drug addicts.
The solution is no more valid concerning protection against accidental punctures as known at present, and which consists of fitting these syringes with sheaths wrapped around the needle. As now given, this protective sheath will guarantee the asepsis of the needle while the preliminary operations of preparation of the solution to be rejected are carried out, therefore accidental punctures are not prevented this way.
Thus, it is the aim of this invention to provide a hypodermic syringe of the above-mentioned type, that is to say, on the basis of low cost materials which will make them "disposable" and which render themselves irreversibly un-reusable during the action of injecting, that is to say, without the intervention of the will of the user in the process of rendering themselves un-reusable, so that a truly "single use" syringe is provided.
Additionally, it is one of the aims of the invention to provide a syringe of this type that has a device for protection of the needle, so as to eliminate or at least decrease the possibility of accidental punctures with the needle.
With this invention such aims are attained since this syringe, having plunger and barrel portions with a plunger stem that has a rupture point located near its distal end, is provided with the following:
Means for turning placed in a cooperating manner on the aforesaid plunger and/or barrel parts so that when the plunger moves forward during the injection it causes the relative turning of said portions; PA0 Means for blocking the turn of the stem placed in a cooperating manner on the inner wall of the said barrel and/or plunger parts that prevent the simultaneous or solidary turning of the two sections of the plunger stem located on either side of the point or line of rupture, so that as the plunger moves during the injection there is between the two sections of the stem sufficient torque to cause the rupture of the stem at this rupture point; and PA0 Means for coupling, acting like a clutch, located at either end of the stem of the plunger section, which with the backward or upward motion of the plunger stem during the suction of the substance to be injected, uncouple the aforementioned means for turning the stem in such a way that the aforesaid turning motion does not take place. The torque is thereby eliminated and consequently the stem does not rupture during the loading of the syringe.
In an embodiment of the invention, the means for turning the plunger stem consists of a part coaxially coupled to the upper part of the plunger stem on whose periphery there are longitudinal fillets cooperating with helicoidal grooves made in the inner wall of the upper part of the barrel section. In this embodiment the means for blocking consists of longitudinal fillets placed on the inside wall of the distal end of the barrel section of the syringe, adjacent to the end part of the stem, i.e., the plunger itself which as is well known, is normally made of some elastic material such as rubber. Thus, the turning of this section of the stem is prevented, since the rubber part cannot slide over the aforementioned fillets.
In this embodiment, the means for coupling is a fleam tooth clutch consisting of indentations placed in a complementary position at the upper end of the stem and on the aforesaid part coaxial with it that determines the means for turning. As will easily be understood by those skilled in the art, in order to achieve the uncoupling of the aforesaid clutch during the backward motion of the plunger stem in the course of the suction of the solution to be injected, it is necessary that there be some play between the longitudinal fillets of the aforesaid coaxial part and the helicoidal grooves located on the upper inner wall of the barrel. Furthermore, between the plunger stem and the part coaxially coupled to it there must also be some longitudinal play.
In another embodiment of the invention the means for causing the rotation of the plunger stem will be located on the lower or distal section of the syringe in the form of helicoidal grooves made in the inner wall of the barrel and cooperating with the longitudinal fillets of the distal or lower end of the plunger stem. In this case, the means for blocking the turn will consist of grooves and cooperating fillets located on the upper part of the stem and upper inner wall of the barrel part. For this embodiment the means for coupling, also in the form of a fleam tooth clutch, must be located near the end of the plunger stem.
In another embodiment of the invention the means for causing the turning of the stem are constituted jointly by a plunger stem having the configuration of a screw and a guiding piece coaxially coupled to it, with a cruciform opening, so that the stem is forced to turn as it goes through the cruciform opening. In this embodiment, the means for blocking the turn of the stem are also made up by fillets on the inner wall of the syringe barrel which brush against the rubber plunger. In this case too, the means for coupling that allow the backward or upward motion of the plunger stem during the suction of the substance to be injected consists of a fleam tooth clutch located on the lower part of the plunger stem.